ci(deploy): event-driven prod deploy via Forgejo Actions on push to main

On a push to main the server-hosted runner SSHes back to the host (forced-command
key, docker bridge gateway, port 2222) and runs deploy/deploy.sh — replacing the
2-minute systemd poller. Build/publish still happens on the dev machine before push.

.forgejo/workflows/deploy.yml

@@ -0,0 +1,32 @@
+name: deploy
+
+# Event-driven production deploy. Replaces the 2-minute systemd poller on asgard: on a push
+# to main, the asgard-hosted Forgejo Actions runner connects back to the asgard host over the
+# Docker bridge gateway and runs the existing deploy/deploy.sh, which pulls the published image
+# and restarts the stack. The image itself is still built and pushed from the developer machine
+# (`siftlode publish`) BEFORE the push — this job only triggers the deploy, it does not build.
+#
+# The SSH key is a dedicated, forced-command key on the host (it can ONLY run deploy.sh), stored
+# here as a base64-encoded Actions secret. The host address is the container's default-route
+# gateway (= the Docker host), resolved at runtime so no fixed IP or runner config is needed.
+
+on:
+  push:
+    branches: [main]
+
+jobs:
+  deploy:
+    runs-on: ubuntu-latest
+    steps:
+      - name: trigger host deploy
+        run: |
+          command -v ssh >/dev/null 2>&1 || { apt-get update -qq && apt-get install -y -qq openssh-client; }
+          install -m 700 -d ~/.ssh
+          printf '%s' "${{ secrets.DEPLOY_SSH_KEY_B64 }}" | base64 -d > ~/.ssh/id_ed25519
+          chmod 600 ~/.ssh/id_ed25519
+          # Default-route gateway of this job container = the Docker host (little-endian hex in /proc/net/route).
+          H=$(awk '$2=="00000000" && $1!="lo"{print $3; exit}' /proc/net/route)
+          HOST=$(printf '%d.%d.%d.%d' "0x${H:6:2}" "0x${H:4:2}" "0x${H:2:2}" "0x${H:0:2}")
+          echo "Deploying via host $HOST:2222"
+          ssh -p 2222 -o StrictHostKeyChecking=accept-new -o UserKnownHostsFile=/dev/null \
+              -i ~/.ssh/id_ed25519 "p33t@$HOST" deploy